This invention relates to a method of and an apparatus for cleaning the air in clean rooms, clean booths, clean tunnels, clean benches, safety cabinets, aseptic rooms, bath boxes, aseptic air curtains, or clean tubes in the electronics industry, medicines industry, food industry, agricultural and forestry industries, medical facilities and precision machine industries.
Conventional air cleaning methods or apparatus in a room are generally classified into the following:
(1) a mechanical filter type (e.g., a HEPA filter), and PA1 (2) a filtering type which charges fine particles electrically at a high voltage and collecting the particles electrostatically by means of a conductive filter (e.g., a MESA filter). PA1 (1) The charging of fine particles in the air can be efficiently performed as compared with the conventional electrostatic filter type; PA1 (2) Since the fine particles are efficiently charged, high quality air, i.e., air of high cleaning class can be provided merely by disposing a collector of suitable charged particles such as an electrostatic filter at the trailing stream side; PA1 (3) Since ultrafine particles are collected by electrically charging, a superclean room can be obtained; and PA1 (4) Since in comparison with the conventional electrostatic ultrafine particle collecting type, a high voltage is not necessary, it is safe and costs less to maintain and manage. PA1 (1) Sterilized clean air is obtained; PA1 (2) It is particularly effective in a field for affecting the influence of the presence of microorganism, like a biotechnologic field; and PA1 (3) The collection of charged particles may not be so restrictive in a biotechnologicl relation, i.e., small leakage is allowed to provide an inexpensive apparatus.
These types have the following drawbacks:
In the mechanical filter type, it is necessary to use a fine filter to improve the quality (the cleaning class) of the air. In this case, the pressure loss is high, the increase in pressure loss due to clogging is remarkable, the lifetime of the filter is short, and the maintenance, the management and the exchange of the filter are complicated. When the filter is exchanged, it is necessary to stop working during the exchange, and it takes a long time to recover the system which deteriorates the production efficiency.
The number of times for ventilations (the number of times for circulating the air by a fan) is increased to improve the quality, i.e., to raise the cleaning class of the air, but the cost of power increases.
Since the only purpose of the conventional filter method is to remove fine particles, it can be used as an industrial clean room, but as the filter always has pin-holes which leak part of the contaminated air, its use in a biological clean room is limited.
In the type for electrostatically collecting fine particles, a high voltage such as 15 to 70 kV is necessary in a preliminary charger to cause the system to increase in size, and there are safety, maintenance and management drawbacks.
In order to solve the above mentioned drawbacks, the inventor of the present invention has proposed an air cleaning system by irradiation of ultraviolet rays (Japanese Patent Application No. 216293/1984). Such a system is effective for a certain application field and utility, but is insufficient if applied to the purification of air containing ultrafine particles and any special field.